Turbocharger Turbine Assembly

ABSTRACT

A turbocharger including a turbine housing including a gas inlet passage and a turbine wheel arranged in the turbine housing. A bearing housing is connected to the turbine housing. A nozzle ring is disposed around the turbine wheel and a shroud is arranged in surrounding relation to at least a portion of the turbine wheel. The shroud is connected to the nozzle ring and the nozzle ring and shroud are connected to a heat shield. The heat shield is secured to the bearing housing by a plurality of cross key pins, each cross key pin being inserted in a radially extending first passage in the heat shield and a complementary radially extending second passage in the bearing housing. The first passages and second passages are symmetrically arranged in a circular pattern about a rotational axis of the turbine.

TECHNICAL FIELD

This disclosure relates generally to turbochargers for use with internalcombustion engines and, more particularly, to a turbine assembly for aturbocharger.

BACKGROUND

Internal combustion engines are supplied with a mixture of air and fuelfor combustion within the engine that generates mechanical power. Tomaximize the power generated by this combustion process, the engine isoften equipped with a turbocharged air induction system. A turbochargedair induction system includes a turbocharger that uses exhaust from theengine to compress air flowing into the engine, thereby forcing the airinto a combustion chamber of the engine than the engine could otherwisedraw into the combustion chamber. This increased supply of air allowsfor increased fueling, resulting in an increased engine power output.

A turbocharger generally comprises a compressor wheel mounted on one endof a single shaft in a compressor housing and a turbine wheel mounted onthe other end of the shaft in a turbine housing. Typically, the turbinehousing is formed separately from the compressor housing. A bearinghousing is connected between the turbine and compressor housings forcontaining bearings for the shaft. The turbine housing receives exhaustgas from the engine and directs it to the turbine wheel which is drivenby the exhaust gas. The turbine assembly thus extracts power from theexhaust gas and drives the compressor.

Turbines rotate at very high speed. Conventional turbine assemblies useradial pins to force symmetrical expansion of hot housings relative tothe centerline of the turbocharger in order to achieve uniform tipclearances between the high speed rotating turbine wheel and thestationary housing components of the turbine assembly. However, the pinsare subject to wear as the housings expand and contract due to heat.Moreover, the pins can also bind if the loads on them are too high ornon-uniform.

SUMMARY

In one aspect, the disclosure describes a turbocharger comprising aturbine housing including a gas inlet passage and a turbine wheel thathas a plurality of blades and is arranged in the turbine housing. Abearing housing is connected to the turbine housing. A shaft isrotatably supported in the bearing housing and connected to the turbinewheel. The turbocharger also include a heat shield and a nozzle ringdisposed around the turbine wheel and including a plurality of vaneswith flow channels being defined between the vanes that are in fluidcommunication the gas inlet passage and with the turbine wheel. A shroudis arranged in surrounding relation to at least a portion of the turbinewheel. The shroud is connected to the nozzle ring and the nozzle ringand shroud are connected to the heat shield. The heat shield is securedto the bearing housing by a plurality of cross key pins. Each cross keypin is inserted in a radially extending first passage in the heat shieldand a complementary radially extending second passage in the bearinghousing. The first passages and second passages are symmetricallyarranged in a circular pattern about a rotational axis of the turbinewheel such that the cross key pins force symmetrical thermal expansionof the heat shield, nozzle ring and shroud during operation of theturbocharger.

In another aspect, the disclosure describes a method of providingsymmetrical thermal expansion of components of a turbocharger includinga turbine housing and a turbine wheel arranged in the turbine housingand connected to a shaft that is rotatably supported in a bearinghousing. The method includes the step of providing a nozzle ringdisposed around the turbine wheel and including a plurality of vaneswith flow channels being defined between the vanes that are in fluidcommunication the gas inlet passage and with the turbine wheel. A shroudarranged in surrounding relation to at least a portion of the turbinewheel is connected to the nozzle ring. The shroud and the nozzle ringare connected to a heat shield. The heat shield is connected to thebearing housing with a plurality of cross key pins, each cross key pinbeing inserted in a radially extending first passage in the heat shieldand a complementary radially extending second passage in the bearinghousing. The first passages and second passages are symmetricallyarranged in a circular pattern about a rotational axis of the turbinewheel such that the cross key pins force symmetrical thermal expansionof the heat shield, nozzle ring and shroud during operation of theturbocharger.

In yet another aspect, the disclosure describes an internal combustionengine having a plurality of combustion chambers formed in a cylinderblock, an intake manifold disposed to provide air or a mixture of airwith exhaust gas to the combustion chambers, and an exhaust manifolddisposed to receive exhaust gas from the combustion chambers. The enginefurther including a turbine housing including a gas inlet passage and aturbine wheel that has a plurality of blades and is arranged in theturbine housing. A bearing housing is connected to the turbine housingand a shaft rotatably supported in the bearing housing and connected tothe turbine wheel. The engine also includes a heat shield and a nozzlering disposed around the turbine wheel and including a plurality ofvanes with flow channels being defined between the vanes that are influid communication the gas inlet passage and with the turbine wheel. Ashroud is arranged in surrounding relation to at least a portion of theturbine wheel. The shroud is connected to the nozzle ring and the nozzlering and shroud are connected to the heat shield. The heat shield issecured to the bearing housing by a plurality of cross key pins, eachcross key pin being inserted in a radially extending first passage inthe heat shield and a complementary radially extending second passage inthe bearing housing. The first passages and second passages beingsymmetrically arranged in a circular pattern about a rotational axis ofthe turbine wheel such that the cross key pins force symmetrical thermalexpansion of the heat shield, nozzle ring and shroud during operation ofthe turbocharger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an internal combustion engine in accordancewith the disclosure.

FIG. 2 is an outline view from a side perspective of a turbocharger inaccordance with the disclosure.

FIG. 3 is a fragmented view through a center of the turbocharger shownin FIG. 2.

FIG. 4 is a detail section of the turbine assembly of the turbochargershown in FIG. 2.

FIG. 5 is a further detail section of the turbine assembly of theturbocharger shown in FIG. 2.

FIG. 6 is a perspective view of a section of the turbine assembly of theturbocharger shown in FIG. 2 with the turbine housing removed.

FIG. 7 is a sectional view of the nozzle ring and turbine wheel of theturbine assembly of the turbocharger shown in FIG. 2.

FIG. 8 is a sectional view of the turbine assembly of the turbochargershown in FIG. 2 taken through the radial cross key pins.

DETAILED DESCRIPTION

This disclosure relates to an improved turbocharger used in conjunctionwith an internal combustion engine to promote the engine's efficientoperation and also the robust and reliable operation of theturbocharger. A simplified block diagram of an engine 100 is shown inFIG. 1. The engine 100 includes a cylinder case 104 that houses aplurality of combustion cylinders 106. In the illustrated embodiment,six combustion cylinders are shown in an inline or “I” configuration,but any other number of cylinders arranged in a different configuration,such as a “V” configuration, may be used. The plurality of cylinders 106is fluidly connected via exhaust valves (not shown) to first and secondexhaust conduits 108 and 110. Each of the first and second exhaustconduits 108 and 110 is connected to a turbine assembly 120 of aturbocharger 119. In the illustrated embodiment, the turbine assembly120 includes a housing 122 having a gas inlet 124, which is fluidlyconnected to the first and second exhaust conduits 108 and 110 andarranged to receive exhaust gas therefrom. Exhaust gas provided to theturbine assembly 120 causes a turbine wheel (not shown in FIG. 1)connected to a shaft 126 to rotate. Exhaust gas exits the housing 122 ofthe turbine assembly 120 through an outlet 128. The exhaust gas at theoutlet 128 is optionally passed through other exhaust after-treatmentcomponents and systems such as an after-treatment device 130 thatmechanically and chemically removes combustion byproducts from theexhaust gas stream, and/or a muffler 132 that dampens engine noise,before being expelled to the environment through a stack or tail pipe134.

Rotation of the shaft 126 causes a compressor wheel (not shown inFIG. 1) of a compressor assembly 136 to rotate. As shown, the compressorassembly 136 may be a radial, mixed-flow or axial compressor configuredto receive a flow of fresh, filtered air from an air filter 138 througha compressor inlet 140. Pressurized air at an outlet 142 of thecompressor assembly 136 is routed via a charge air conduit 144 to acharge air cooler 146 before being provided to an intake manifold 148 ofthe engine 100. In the illustrated embodiment, air from the intakemanifold 148 is routed to the individual cylinders 106 where it is mixedwith fuel and combusted to produce engine power.

An optional EGR system 102 includes an optional EGR cooler 150 that isfluidly connected to an EGR gas supply port 152 of the first exhaustconduit 108. A flow of exhaust gas from the first exhaust conduit 108can pass through the EGR cooler 150 where it is cooled before beingsupplied to an EGR valve 154 via an EGR conduit 156. The EGR valve 154may be electronically controlled and configured to meter or control theflow rate of the gas passing through the EGR conduit 156. An outlet ofthe EGR valve 154 is fluidly connected to the intake manifold 148 suchthat exhaust gas from the EGR conduit 156 may mix with compressed airfrom the charge air cooler 146 within the intake manifold 148 of theengine 100.

The pressure of exhaust gas at the first exhaust conduit 108, which iscommonly referred to as back pressure, is higher than ambient pressure,in part, because of the flow restriction presented by the turbineassembly 120. For the same reason, a positive back pressure is presentin the second exhaust conduit 110. The pressure of the air or the air/EGR gas mixture in the intake manifold 148, which is commonly referredto as boost pressure, is also higher than ambient because of thecompression provided by the compressor assembly 136. In large part, thepressure difference between back pressure and boost pressure, coupledwith the flow restriction and flow area of the components of the EGRsystem 102, determine the maximum flow rate of EGR gas that may beachieved at various engine operating conditions.

An outline view of the turbocharger 119 is shown in FIG. 2, and afragmented view is shown in FIG. 3. In reference to these figures, andin the description that follows, structures and features that are thesame or similar to corresponding structures and features alreadydescribed may be, at times, denoted by the same reference numerals aspreviously used for simplicity. As shown, the turbine assembly 120 isconnected to a bearing housing 202. The bearing housing 202 surrounds aportion of the shaft 126 and includes bearings 242 and 243 disposedwithin a lubrication cavity 206 formed within the bearing housing 202.The lubrication cavity 206 includes a lubricant inlet port 203 and alubricant outlet opening 205 that accommodate a flow of lubricationfluid, for example, engine oil, therethrough to lubricate the bearings242 and 243 as the shaft 126 rotates during engine operation.

The shaft 126 is connected to a turbine wheel 212 at one end and to acompressor wheel 213 at another end. The turbine wheel 212 is configuredto rotate within a turbine housing 215 that is connected to the bearinghousing 202. The compressor wheel 213 is disposed to rotate within acompressor housing 217. The turbine wheel 212 includes a plurality ofblades 214 radially arranged around a hub 216. The hub 216 is connectedto an end of the shaft 126. In the illustrated embodiment, the turbinewheel 212 is connected at the end of the shaft 126 by welding, but othermethods, such as by use of a fastener, may be used to connect theturbine wheel to the shaft. The turbine wheel 212 is rotatably disposedbetween an exhaust turbine nozzle 230 defined within the turbine housing215. As described further below, the slot 230 provides exhaust gas tothe turbine wheel 212 in a generally radially inward and axial directionrelative to the shaft 126 and the blades 214 such that the turbineassembly 120 is a mixed flow turbine, meaning, exhaust gas is providedto the turbine wheel in both radial and axial directions. Exhaust gaspassing over the turbine wheel 212 exits the turbine housing 215 via anoutlet bore 234 that is formed in the housing and that is fluidlyconnected to the turbine assembly outlet 128 (FIG. 1). The turbinenozzle 230 is fluidly connected to an inlet gas passage 236 having ascrolled shape and formed in the turbine housing 215. The inlet gaspassage 236 fluidly interconnects the turbine nozzle 230 with theturbine inlet 124 (also see FIG. 1). It is noted that a single inlet gaspassage 236 is shown formed in the turbine housing 215 in FIG. 3, but inalternative embodiments separated passages may be formed in a singleturbine housing.

In the embodiment shown in FIG. 3, the inlet gas passage 236 wrapsaround the area of the turbine wheel 212 and bore 234 and is open to theslot 230 around the entire periphery of the turbine wheel 212. A crosssectional flow area of the inlet gas passage 236 decreases along a flowpath of gas entering the turbine assembly 120 via the inlet 124 andbeing provided to the turbine wheel 212 through the slot 230.

The bearing housing 202 encloses a portion of the shaft 126, which isrotationally mounted in a bearing bore 260 formed in the bearing housingby bearings 242 and 243. A nut 288 engaged on the shaft 126 retains theshaft 126 within the bearings 242 and 243. Each of the bearings 242 and243 includes an outer race 261 that engages an inner diameter surface ofthe bore 260, rollers, and an common inner race 262 that has a generallytubular shape and extends around the shaft 126 along its length. Oilfrom the inlet port 203 is provided by an external oil pump to thebearings 242 and 243 during operation via passages 264, from where itwashes over the bearings to cool and lubricate them before collecting inthe lubrication cavity 206 and draining out of the bearing housingthrough the outlet opening 205.

The bearings 242 and 243 are axially retained within the bore 260 by abearing retainer 266 disposed between a compressor mounting plate 268formed on the bearing housing 202 and the compressor wheel 213. Thebearing retainer 266 forms a central opening 270 having an innerdiameter that is smaller than an inner diameter of the bearing bore 260such that, when the bearing retainer 266 is connected to the bearinghousing 202, the bearings 242 and 243 are retained within the bearingbore 260. The bearing retainer 266 is fastened to the compressormounting plate 268 by fasteners 272, but other fastening or retentionstructures may be used.

The compressor assembly 136 includes a compressor vane ring 274 thatforms vanes 276 disposed radially around the compressor wheel 213. Thevanes 276 fluidly connect a compressor inlet bore 278, which containsthe compressor wheel 213, with a compressor scroll passage 280 that isformed in the compressor housing 217 and that terminates to a compressoroutlet opening 282. Bolts 284 and circular plate segments 286 connectthe turbine housing 215 to the turbine flange 256 and the compressorhousing 217 to the compressor mounting plate 268. A nut 288 engaged onthe shaft 126 retains the shaft 126 within the bearings 242 and 243.

For directing the exhaust air from the inlet gas passage 236 to the areasurrounding the turbine wheel 212, the turbine assembly 120 may includea nozzle ring 238. The nozzle ring 238 may have an annular configurationand extend around a portion of the radial periphery of the turbine wheel212. As will be discussed in more detail in the paragraphs that follow,the radial nozzle ring 238 is disposed in fluid communication with theinlet gas passage 236 and may define at least a portion of the slot 230around the wheel 212. As shown in FIG. 4, the radial nozzle ring 238forms a plurality of fixed vanes 246 that are symmetrically disposedaround the nozzle ring 238 and operate to direct exhaust gas from theinlet gas passage 236 towards the turbine wheel 212. The number, shapeand configuration of the plurality of vanes 246 can vary. Flow channels250 having an inclined shape are defined between adjacent vanes 246. Asshown in FIG. 6, the vanes 246 may further have a generally curvedairfoil shape to minimize flow losses of gas passing over and betweenthe vanes, thus providing respectively uniform inflow conditions to theturbine wheel 212.

To provide protection in the event of failure of the turbine wheel 212and to further define the turbine nozzle 230 that directs exhaust gas tothe turbine wheel, the turbine assembly 120 may further include a shroud290 that surrounds at least a portion of the turbine wheel 212. Theshroud 290 may be spaced outward of the turbine wheel 212 in the radialdirection of the turbine wheel and extend around the entirecircumference of the turbine wheel 212. Further, the shroud 290 mayextend in the axial direction (as defined by the rotational axis of theturbine wheel 212) at least a portion of the axial length of the turbinewheel 212. As shown in FIG. 5, the shroud 290 may include a first leg292 that extends substantially in the radial direction relative to theturbine wheel 212 and a second leg 294 that extends substantially in theaxial direction relative to the turbine wheel 212. The first and secondlegs 292, 294 may be joined together by a curved intermediate portion296. It will be appreciated, however, that the shroud 290 may have aconfiguration different than that shown in the drawings so long as itsurrounds at least a portion of the turbine wheel 212.

According to one embodiment, the nozzle ring 238 may be integrated withthe shroud 290 into a single component as shown in FIGS. 4 and 5. Inparticular, the vanes 246 of the nozzle ring 238 may be integrallyconnected with and extend axially away from the first leg 292 of theshroud 290 towards the bearing housing 202. With this arrangement, thevanes 246 may provide structural support to the shroud 290. Moreover,with such a configuration, the nozzle ring 238 and shroud 290 may becast as a single component. This can allow both the nozzle ring 238 andshroud 290 to be constructed of a single material, which can minimizethermal mismatches between the nozzle ring 238 and the shroud 290 andthereby reduce thermal stresses in the turbine assembly 120.Additionally, integrating the nozzle ring 238 into the shroud 290 mayallow for the use of relatively lower cost cast iron material for thecombined nozzle ring and shroud. One example of a suitable material forthe cast nozzle ring 238 and shroud 290 is high silicon, molybdenumiron, but other materials may be used. The integration of the nozzlering 238 into the shroud 290 also provides a lower part count, which canreduce assembly complexity and cost as well as reduce the time requiredto service or remanufacture the turbine.

As indicated above, the shroud 290 and nozzle ring 238 may be configuredso as to define a so-called mixed flow path from the turbine housinginlet gas passage 236 to the turbine wheel 212 such that wheel rotationmay be augmented. In general, turbines can be configured forradial-flow, axial-flow (for example, such as those used in jetengines), or a hybrid type of flow that includes radial and axialcomponents, which will herein be referred to as “mixed” flow to denotethat the flow includes radial and axial flow characteristics. Withrespect to the illustrated embodiment, as shown in FIGS. 5 and 7, theradial flow component may be provided by the flow channels defined bythe vanes 246 which are arranged and configured to direct gas passingthrough the flow channels defined between the vanes 276 tangentially andradially inward towards an inner diameter of the turbine wheel 212. Inthis portion of the shroud 290, a radial nozzle may be formed. The axialflow component may be provided by the curved intermediate portion 296and the axially extending second leg 294 of the shroud 290 as shown inFIG. 5, which forms a converging axial nozzle along the rotational axisof the turbine, which accelerates the gases past the curved ends of theblades 214 on the turbine wheel. In particular, the curved intermediateportion 296 and the second leg 294 of the shroud 290 may define a flowpath that directs at least a portion of the exhaust gas that travelsthrough and exits the flow channels between the vanes 246 of the nozzlering 238 in a more axial direction as it moves toward the surface of theturbine wheel 212. Turbine assemblies having mixed flow can have a lowerpressure drop of the gas passing through the turbine as compared toradial flow turbine assemblies, because not all of the gases provided todrive the turbine must turn from the radial direction to the axialdirection.

The configuration of the vanes 246 of the nozzle ring 238 and the shroud290 may be adjusted to provide more pronounced radial flow or axial flowcharacteristics to provide a desired turbocharger performance for aparticular engine configuration. For example, to facilitate matching ofthe flow channels 250 of the nozzle ring 238 to each specific enginerating, the nozzle ring 238 and shroud 290 may be cast with excessmaterial in the flow channels 250 such that the flow channels can belater machined to a desired flow channel geometry for optimization ofthe tuning of the nozzle ring 238 to each specific engine rating. Inthis way, the unique flow characteristics of the turbine assembly 120may be determined by the size, shape, number, and configuration of theflow channels 250 in the nozzle ring 238 while other portions of theturbine assembly may advantageously remain unaffected or, in the contextof designing for multiple engine platforms, the remaining portions ofthe turbine assembly may remain substantially common for various enginesand engine applications.

Accordingly, the specific flow characteristics of a turbine assemblythat are suited for a particular engine system may be achieved bycombining a turbine assembly, which otherwise may be common for morethan one engine, with a nozzle ring 238 that has been machined aftercasting to a configuration that is specifically suited for thatparticular engine system. In contrast to casting a variety of differentnozzles to match particular engine systems, casting a commonlyconfigured nozzle ring 238, and then machining the flow channels 250 inthe nozzle ring to the final desired configuration, may be more costeffective and may provide more control over the final configuration ofthe nozzle ring. Selection of the appropriate nozzle ring flow channel250 configuration that corresponds to a particular engine can involvethe consideration of various turbocharger operating conditions, such asexhaust gas temperature, pressure and flow rate, desired pressuredifference to drive the turbine, turbine size, desired turbine A/Rratio, and others.

To help reduce heat transfer from the hot exhaust gas flowing throughthe turbine housing 215 to the bearing housing 202, the turbine assembly120 may be provided with a heat shield 302. The heat shield 302 may bearranged between the bearing housing 202 and the nozzle ring 238 andshroud 290 as shown in FIGS. 4 and 5. More particularly, as shown inFIG. 5, an outer thickened portion 304 of the heat shield 302 may becaptured in a complementary recess 306 in a turbine mounting flange 256on the bearing housing 202 by the nozzle ring 238 and shroud 290.Moreover, a raised portion 308 on the turbine mounting flange 256 canengage in a complementary recess 310 formed in the side of the heatshield 302 facing the bearing housing 202. These features can helplocate the heat shield 302 in the proper position relative to thebearing housing 202 during installation. The heat shield 302 may furtherhave a center opening 312, through which the end of the shaft 126 mayproject. To minimize thermal stresses on the turbine assembly 120, theheat shield 302 may be made of the same material as the nozzle ring 238and shroud 290. As noted previously, an example of a suitable materialof construction for these components is high silicon, molybdenum iron,although other materials also may be used.

The shroud 290 may be spaced apart and separate from the turbine housing122. In particular, as shown in FIGS. 4 and 5, the shroud 290 may bespaced axially inward (i.e., in the direction towards the bearinghousing 202) from the turbine housing 122 so as to provide the turbineassembly 120 with a dual wall construction in the area of the shroud 290with the shroud 290 comprising an inner wall and the turbine housing 122comprising an outer wall. This arrangement isolates the shroud 290, andin this case the integral nozzle ring 238, from the turbine housing 122.The shroud 290 further may be configured and arranged such that it willshear off from the remainder of the turbine assembly 120 upon failure ofthe turbine wheel 212, such as, for example, upon a failure of theinertia weld between the turbine wheel 212 and the shaft 126. To thisend, the shroud 290 and nozzle ring 238 may be secured in the turbineassembly 120 using a fastening arrangement that is configured to breakor shear when a force is exerted on the shroud 290 corresponding to theforce that would be exerted on the shroud 290 upon failure of theturbine wheel 212. For example, the shroud 290 may be connected to theturbine assembly 120 using one or more fasteners that are configured toshear when a predetermined force is applied to the shroud 290 either inthe axial and/or the radial direction(s).

In the illustrated embodiment, the shroud 290 and, in this case, theintegral nozzle ring 238, are connected to the heat shield 302 by aplurality of shear bolts 314. As described above, the heat shield 302,in turn, is fixed relative to the bearing housing 202. Thus, the shearbolts 314 fix the shroud 290 relative to the heat shield 302 and thebearing housing 202 and hold the shroud 290 stationary relative to therotating turbine wheel 212. As shown in FIG. 5, each shear bolt 314 mayhave a corresponding nut 316 secured to the shear bolt at the end of thebolt protruding through the heat shield 302. Additionally, a springwasher 318 may be arranged at each end of the shear bolt 314. The springwashers 318 may help the shear bolts 314 compensate for thermalexpansion lag of the components of the turbine assembly 120 duringoperation. For example, the shear bolts 314, which are not directlyexposed to hot gases, may thermally expand after surrounding structures,which are in direct contact with hot gases, have already expanded.Moreover, depending on the materials used, the thermal expansioncoefficient between the shear bolts 314 and the surrounding structuresmay differ.

Additionally, the turbine assembly 120 may be configured such that theshear bolts 314 and associated nuts 316 are trapped in the turbineassembly 120 in such a way that the nuts 316 and shear bolts 316 cannotseparate from each other during operation of the turbocharger 119. Inparticular, as shown in FIG. 5, the head of each shear bolt 314 may becaptured between the first leg 292 of the shroud 290 and the turbinehousing 215 and each associated nut 316 may be captured on the end ofthe corresponding shear bolt 314 by being interposed between the heatshield 302 and the bearing housing 202. As shown in FIG. 7, each of theshear bolts may extend from the shroud 290 to the heat shield 302through a corresponding one of the vanes 246 of the nozzle ring 238. Tothis end, each of the vanes 246 that are to receive one of the shearbolts may have a passage extending in the axial direction of the turbineassembly through the vane 246 within which the respective shear bolt 314may be inserted.

In operation, the shear bolts 314 will fracture when the turbine wheel212 fails in such a manner that the rotating turbine wheel 212, orfragments thereof, comes into contact with the shroud 290. Thefracturing of the shear bolts 314 can allow the shroud 290 to rotatewithin the turbine housing 215 with the still rotating broken turbinewheel 212. The rotating shroud 290 can help dissipate the energy of thebroken turbine wheel 212 in a similar manner to that of a brake pad in afriction drum brake. Additionally, when the shear bolts 314 shear,producing the acceleration necessary to overcome the rotational inertiaof the shroud 290 will also absorb energy generated by the failure ofthe turbine wheel 212. The energy absorbed by setting the shroud 290into rotation and the braking action of the shroud 290 on the turbinehousing 215 can help reduce the likelihood of a turbine wheel 212 burstand/or exit through the turbine housing 215. The use of the dual wallstructure comprising the turbine housing 215 as the outer wall and theseparate shroud 290 as the inner wall distributes the force of theturbine wheel 212 fragments in a turbine wheel failure situationallowing for the use of a thinner, lighter weight turbine housing 215.The force at which the shroud 290 shears from the heat shield 302 may beadjusted by varying the number of shear bolts 314, the diameter of theshear bolts and/or the material of the shear bolts. As can be seen fromFIG. 7, a total of five shear bolts 314 are used in the illustratedembodiment to secure the shroud 290 to the heat shield 302. According toother embodiments, there may as few as three and as many as fifteenshear bolts 314. As will be appreciated, the present disclosure is notlimited to any particular number of shear bolts 314. According to oneembodiment, each of the shear bolts 314 may have a 0.187 inch diameterand be made of an alloy suitable for high temperature applications suchas alloys sold under the trade name Waspaloy®. The separate, shearableshroud 290 may be configured with an integral nozzle ring 238 or may beconfigured such that the nozzle ring is a separate component.

To help ensure symmetrical thermal expansion of various componentsincluding the heat shield 302, the nozzle ring 238 and the shroud 290during operation of the turbocharger 119, the heat shield 302 may besecured to the bearing housing with a plurality of symmetricallyarranged stakes or radial cross key pins 320. The heat shield 302 mayfirst be arranged on the turbine mounting flange 256 of the bearinghousing 202 with an interference fit and then secured in place with theradial cross key pins 320. Each of the cross key pins 320 may bereceived in a corresponding one of a plurality of circumferentiallyspaced radially extending passages 322 in the thickened outer portion304 of the heat shield 302 and into complementarily arranged passages324 in the turbine mounting flange 256 of the bearing housing 202. Thepassages 322, 324 in the heat shield 302 and the turbine mounting flange256 for receiving the cross key pins 320 (and the inserted cross keypins) are arranged symmetrically in a circular pattern about therotational axis of the turbine wheel 212 as shown in FIG. 8 whichprovides a cross-sectional view through the heat shield 302 and pins320. A single cross key pin 320 extending in the radial directionthrough the heat shield 302 and into the bearing housing 202 can be seenin FIG. 4 and the outer ends of several of the cross key pins 320 can beseen in FIG. 6.

As noted above, the shroud 290 and integral nozzle ring 238 may beattached to the heat shield 302 by, for example, the shear bolts 314.The heat shield 302 is, in turn, attached to the bearing housing 202through the cross key pins 320. As a result, the heat shield 302, shroud290 and nozzle ring 238 are connected together as a system. Further, thecross key pins 320 keep the heat shield 302, nozzle ring 238 and shroud290 substantially concentric as well as keep the heat shield 302retained to the bearing housing 202 over the thermal operating range ofthe turbocharger 119. More particularly, during operation of theturbocharger 119, the interconnection between the bearing housing 202and the heat shield 302 established by the cross key pins 320 forces theheat shield 302, and with it the interconnected shroud 290 and nozzlering, to stay concentric even when a temperature differential existsbetween the bearing housing 202 and the heat shield 302. For example,during operation of the turbocharger 119, the temperature of the bearinghousing 202 at the turbine mounting flange 256 may be approximately 400°C. while the temperature of the heat shield 302 is approximately 700° C.The cross key pins 320 can keep the heat shield 302, shroud 290 andnozzle ring 238 concentric with respect to the turbine wheel 212 despitesuch a temperature differential.

The joining together of the heat shield 302, nozzle ring 238 and shroud290 as a system can also help enable minimal loading on the cross keypins 320 and loads on the cross key pins that are symmetric. Further,constructing the shroud 290, nozzle ring 238 and heat shield 302 fromthe same material may avoid the generation of loads and stresses on thecross key pins 320 due to thermal mismatching of mating components.Making the nozzle ring 238 and shroud 290 as a single integralcomponent, as discussed above, may further ensure symmetric loads on thecross key pins 320. Each of these features can allow for cross keying ofthe heat shield 302, nozzle ring 238 and shroud 290 without excessivedistress and wear on the cross key pins 320.

As shown in FIG. 4, the passages 322, 324 in the heat shield 302 andbearing housing 202 for receiving the cross key pins 320 may be arrangedsuch that the cross key pins 320, once inserted in their respectivepassages, are trapped by the turbine housing 215 such that the cross keypins 320 cannot pull out of their respective passages during operationof the turbocharger 119. In particular, an interior wall 326 of theturbine housing 215 may be arranged opposite the radially outward end ofthe cross key pins 320 so as block movement of the cross key pins out oftheir respective passages 322, 324. As shown in FIG. 8, the illustratedembodiment includes a total of fifteen radial cross key pins 320.However, a different number of cross key pins 320 may be provided solong as they are arranged symmetrically about the centerline of theturbine assembly 120. The pins may be made of any material suitable forhigh temperature applications, such as, for example, stainless steel.

To help seal against external leak of exhaust gases from within theturbine housing 215, the turbine assembly 120 may include one or moreexhaust gas seals. For example, a first exhaust gas seal 328 may bearranged between the turbine shroud 290 and the turbine housing 215. Asshown in FIG. 5, the first exhaust gas seal 328 may extend between thesecond leg 294 of the shroud 290 and the inside wall of the turbinehousing 215. In this position, the first exhaust gas seal 328 mayprevent exhaust gas from bypassing the flow channels 250 in the nozzlering 238 and escaping to the outlet bore 234 through the space betweenthe shroud 290 and the turbine housing 215. A second exhaust gas seal330 may further be arranged between the heat shield 302 and the bearinghousing 202. The second exhaust gas seal 330 may comprise a plurality ofknife edge seals on the side of the heat shield 302 facing the turbinemounting flange 256 of the bearing housing 202. The knife edge seals ofthe second exhaust gas seal 330 may extend into engagement with theturbine mounting flange 256. The locations of the first and secondexhaust gas seals 328, 330 shown in FIG. 5 can help achieve a pressurebalance across the nozzle ring 238, shroud 290 and heat shield 302assembly at maximum turbine pressures which, in turn, can further helpminimize loading on the cross key pins 320. As will be appreciated bythose skilled in the art, additional seals and alternative sealingarrangements may also be provided.

INDUSTRIAL APPLICABILITY

It will be appreciated that the foregoing description provides examplesof the disclosed system and technique. However, it is contemplated thatother implementations of the disclosure may differ in detail from theforegoing examples. All references to the disclosure or examples thereofare intended to reference the particular example being discussed at thatpoint and are not intended to imply any limitation as to the scope ofthe disclosure more generally. All language of distinction anddisparagement with respect to certain features is intended to indicate alack of preference for those features, but not to exclude such from thescope of the disclosure entirely unless otherwise indicated.

It will be appreciated that the foregoing description provides examplesof the disclosed system and technique. All references to the disclosureor examples thereof are intended to reference the particular examplebeing discussed at that point and are not intended to imply anylimitation as to the scope of the disclosure more generally. Alllanguage of distinction and disparagement with respect to certainfeatures is intended to indicate a lack of preference for thosefeatures, but not to exclude such from the scope of the disclosureentirely unless otherwise indicated.

Accordingly, this disclosure includes all modifications and equivalentsof the subject matter recited in the claims appended hereto as permittedby applicable law. Moreover, any combination of the above-describedelements in all possible variations thereof is encompassed by thedisclosure unless otherwise indicated herein or otherwise clearlycontradicted by context.

We claim:
 1. A turbocharger comprising: a turbine housing including agas inlet passage; a turbine wheel that has a plurality of blades and isarranged in the turbine housing; a bearing housing connected to theturbine housing; a shaft rotatably supported in the bearing housing andconnected to the turbine wheel; a heat shield; a nozzle ring disposedaround the turbine wheel and including a plurality of vanes with flowchannels being defined between the vanes that are in fluid communicationthe gas inlet passage and with the turbine wheel; and a shroud arrangedin surrounding relation to at least a portion of the turbine wheel, theshroud being connected to the nozzle ring, the nozzle ring and shroudare connected to the heat shield; wherein the heat shield is secured tothe bearing housing by a plurality of cross key pins, each cross key pinbeing inserted in a radially extending first passage in the heat shieldand a complementary radially extending second passage in the bearinghousing, the first passages and second passages being symmetricallyarranged in a circular pattern about a rotational axis of the turbinewheel such that the cross key pins force symmetrical thermal expansionof the heat shield, nozzle ring and shroud during operation of theturbocharger.
 2. The turbocharger of claim 1 wherein the shroud isintegrally formed with the nozzle ring such that the plurality of vanesextend away from the shroud.
 3. The turbocharger of claim 1 wherein theshroud, the nozzle ring and the heat shield are made of the samematerial.
 4. The turbocharger of claim 1 wherein the flow channelsdefined by the vanes are configured to direct gas tangentially andradially inward toward an inner diameter of the turbine wheel and theshroud is configured to define a flow path in communication with the gasinlet passage and the flow channels, the flow path extending in adirection substantially parallel to a rotational axis of the turbinewheel.
 5. The turbocharger of claim 4 wherein the shroud includes afirst leg that extends in a radial direction of the turbine wheel and asecond leg that extends in the direction substantially parallel to therotational axis of the turbine wheel.
 6. The turbocharger of claim 5wherein the vanes extend from the first leg of the shroud.
 7. Theturbocharger of claim 5 further including a first gas seal arrangedbetween the second leg of the shroud and an inside wall of the turbinehousing.
 8. The turbocharger of claim 7 further including a second gasseal arranged between the heat shield and the bearing housing.
 9. Theturbocharger of claim 8 wherein the second seal comprises a plurality ofknife edge seals that extend from a surface of the heat shield intoengagement with the bearing housing.
 10. A method of providingsymmetrical thermal expansion of components of a turbocharger includinga turbine housing and a turbine wheel arranged in the turbine housingand connected to a shaft that is rotatably supported in a bearinghousing, the method comprising: providing a nozzle ring disposed aroundthe turbine wheel and including a plurality of vanes with flow channelsbeing defined between the vanes that are in fluid communication the gasinlet passage and with the turbine wheel; and connecting a shroudarranged in surrounding relation to at least a portion of the turbinewheel to the nozzle ring; connecting the shroud and the nozzle ring to aheat shield; connecting the heat shield to the bearing housing with aplurality of cross key pins, each cross key pin being inserted in aradially extending first passage in the heat shield and a complementaryradially extending second passage in the bearing housing, the firstpassages and second passages being symmetrically arranged in a circularpattern about a rotational axis of the turbine wheel such that the crosskey pins force symmetrical thermal expansion of the heat shield, nozzlering and shroud during operation of the turbocharger.
 11. The method ofclaim 10 wherein the shroud is integrally formed with the nozzle ringsuch that the plurality of vanes extend away from the shroud.
 12. Themethod of claim 10 wherein the shroud, the nozzle ring and the heatshield are made of the same material.
 13. The method of claim 11 whereinthe flow channels defined by the vanes are configured to direct gastangentially and radially inward toward an inner diameter of the turbinewheel and the shroud is configured to define a flow path incommunication with the gas inlet passage and the flow channels, the flowpath extending in a direction substantially parallel to a rotationalaxis of the turbine wheel.
 14. The method of claim 13 wherein the shroudincludes a first leg that extends in a radial direction of the turbinewheel and a second leg that extends in the direction substantiallyparallel to the rotational axis of the turbine wheel.
 15. The method ofclaim 14 further including providing a first gas seal arranged betweenthe second leg of the shroud and an inside wall of the turbine housing.16. The method of claim 15 further including providing a second gas sealarranged between the heat shield and the bearing housing.
 17. Aninternal combustion engine having a plurality of combustion chambersformed in a cylinder block, an intake manifold disposed to provide airor a mixture of air with exhaust gas to the combustion chambers, and anexhaust manifold disposed to receive exhaust gas from the combustionchambers, the engine further comprising: a turbine housing including agas inlet passage; a turbine wheel that has a plurality of blades and isarranged in the turbine housing; a bearing housing connected to theturbine housing; a shaft rotatably supported in the bearing housing andconnected to the turbine wheel; a heat shield; a nozzle ring disposedaround the turbine wheel and including a plurality of vanes with flowchannels being defined between the vanes that are in fluid communicationthe gas inlet passage and with the turbine wheel; and a shroud arrangedin surrounding relation to at least a portion of the turbine wheel, theshroud being connected to the nozzle ring, the nozzle ring and shroudare connected to the heat shield; wherein the heat shield is secured tothe bearing housing by a plurality of cross key pins, each cross key pinbeing inserted in a radially extending first passage in the heat shieldand a complementary radially extending second passage in the bearinghousing, the first passages and second passages being symmetricallyarranged in a circular pattern about a rotational axis of the turbinewheel such that the cross key pins force symmetrical thermal expansionof the heat shield, nozzle ring and shroud during operation of theturbocharger.
 18. The engine of claim 17 wherein the shroud, the nozzlering and the heat shield are made of the same material.
 19. The engineof claim 17 wherein the flow channels defined by the vanes areconfigured to direct gas tangentially and radially inward toward aninner diameter of the turbine wheel and the shroud is configured todefine a flow path in communication with the gas inlet passage and theflow channels, the flow path extending in a direction substantiallyparallel to a rotational axis of the turbine wheel.
 20. The engine ofclaim 17 wherein the shroud is integrally formed with the nozzle ringsuch that the plurality of vanes extend away from the shroud.